A study from New Zealand has found that mares with infertility issues may be affected by multi-drug resistant Streptococcus equi subsp. zooepidemicus (S. zooepidemicus). S. zooepidemicus is often associated with inflammation of the lining of the uterus (endometritis) in horses.
Led by Dr. Francesca Paola Nocera, a group of scientists wanted to isolate the S. zooepidemicus strains affiliated with bacterial endometritis in mares and characterize the antimicrobial resistance profile. The team took uterine swabs from 96 mares that had fertility issues. They obtained 23 S. zooepidemicus isolates (a prevalence of 11.7 percent).
S. zooepidemicus is an opportunistic pathogen; it has also been isolated in horses with respiratory infections, which often occur during times of stress, like those found during transport, viral infection or high temperatures
S. zooepidemicus often causes a subclinical infection in uterine tissue that resists the horse's immune response and drug treatment by surviving in epithelial cells as persister cells. These cells aren't affected by antibiotics and resume normal growth.
Antibiotic misuse has also contributed to S. zooepidemicus resistance to multiple drugs.
The antibiotic resistance profiles of the isolates showed the following percentages of resistance: amikacin (95.6 percent), ampicillin (73.98 percent) and tetracycline (69.6 percent). Ceftiofur and ceftriaxone were found to be highly effective.
Alarmingly, 82.6 percent of the total isolated showed resistance to more than three classes of antimicrobials.
Many veterinarians use penicillin as a drug of choice to combat S. zooepidemicus infection, but the study showed a 34.8 percent value of resistance to the antibiotic.
The researchers conclude that escalating multi-drug resistance of S. zooepidemicus has become a relevant veterinary issue and that continuous surveillance of the pathogen is necessary. A proper diagnosis and appropriate antimicrobial choice is necessary, they concluded.
Read more at HorseTalk.
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